Low reactive operation mode and method of direct current transmission converter valve

Abstract

The invention discloses a low reactive power operation mode and method for a direct current transmission converter valve, and the low reactive power operation mode is configured as follows: monitoring the real-time conduction current of a bridge arm of a converter in real time, and when the real-time conduction current of the bridge arm is smaller than the turn-off current, turning off a corresponding turn-off pipe valve string, and turning off the corresponding turn-off pipe valve string. The converter valve continuously operates in the low reactive operation mode, and the current can be turned off before natural zero crossing, so that the extinction angle of the converter valve can be reduced to 0 or even a negative number, the reactive demand of the converter valve is reduced, and reactive stations of the converter valve are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and in particular to a low reactive power operation mode and method of a DC transmission converter valve. Background Art

[0002] With the development of power systems, high voltage direct current transmission technology has become popular due to its advantages in long-distance and large-capacity transmission. Among them, the traditional grid-commutated converter direct current transmission technology (Line-Commutated Converter based high voltage direct current, LCC-HVDC) has more obvious advantages in this regard.

[0003] The existing converter valve must operate at an arc extinction angle of about 17°, otherwise commutation failure will occur, increasing the reactive power demand of the converter valve. Summary of the invention

[0004] In order to solve the above problems, the inventors have made the present invention, and provide a low reactive power operation mode and method for a DC transmission converter valve through a specific implementation method.

[0005] In a first aspect, an embodiment of the present invention provides a low reactive power operation mode of a DC transmission converter valve, wherein a bridge arm of the converter valve has a shutoff valve string, and the low reactive power operation mode is configured as follows:

[0006] The real-time on-current of the bridge arm of the converter is monitored in real time. When the real-time on-current of the bridge arm is less than the off-current, the corresponding shut-off valve string is shut off. When all the energy generated by the off-current on the commutation reactance is absorbed by the buffer capacitor, the maximum voltage of the buffer capacitor is equal to the arrester action voltage.

[0007] Further, the converter includes multiple identical bridge arms, each bridge arm is composed of a switchable tube valve string, each switchable tube valve string is composed of m switchable tubes connected in series, m is a positive integer greater than 1, wherein the anode of the previous switchable tube is connected in series with the cathode of the next switchable tube; wherein the cathode of the switchable tube at the first end of the switchable tube valve string in the first bridge arm among the multiple bridge arms is connected to the positive pole of the DC voltage, and the anode of the switchable tube at the second end of the switchable tube valve string is connected to the three-phase AC connection point; the cathode of the switchable tube at the first end of the switchable tube valve string in the second bridge arm among the multiple bridge arms is connected to the three-phase AC connection point, and the anode of the switchable tube at the second end of the switchable tube valve string is connected to the negative pole of the DC voltage.

[0008] Furthermore, each bridge arm also includes a thyristor valve string connected in series with the turn-off valve string, each thyristor valve string is composed of k thyristors connected in series, k is an integer greater than or equal to 1, wherein the anode of the previous thyristor is connected to the cathode of the next thyristor to achieve series connection; wherein, in the first bridge arm of the multiple bridge arms, the cathode of the thyristor valve string is connected to the positive electrode of the DC voltage, and the anode of the thyristor valve string is connected to the cathode of the turn-off valve string; in the second bridge arm of the multiple bridge arms, the cathode of the thyristor valve string is connected to the three-phase AC connection point, and the anode of the thyristor valve string is connected to the cathode of the turn-off valve string.

[0009] In a second aspect, an embodiment of the present invention provides a method for low reactive power operation of a DC transmission converter valve, comprising:

[0010] Real-time monitoring of the real-time conduction current of the bridge arm of the converter;

[0011] When the real-time conduction current of the bridge arm is less than the shutdown current, the corresponding shutoff valve string is shut off, wherein when the energy generated by the shutdown current on the commutation reactance is completely absorbed by the buffer capacitor, the maximum voltage of the buffer capacitor is equal to the arrester action voltage.

[0012] Furthermore, the method further comprises the following steps:

[0013] The cut-off current is determined according to the lightning protection action voltage of the converter valve, the commutation reactance and the capacitance of the buffer capacitor.

[0014] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least: the converter valve continuously operates in a low reactive power operation mode, which can shut down the current before it naturally crosses zero. Therefore, the arc extinction angle of the converter valve can be reduced to 0 or even a negative number, thereby reducing the reactive power demand of the converter valve and reducing the reactive power station of the converter valve.

[0015] Other features and advantages of the present invention will be described in the following description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0016] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0018] Figure 1 is a flow chart of a method in an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of the structure of a converter valve in an embodiment of the present invention;

[0020] Figure 3 Schematic diagram of another structure of a converter valve in an embodiment of the present invention;

[0021] Figure 4 It is a simulation diagram of the release capacitor under currents of 250A and 400A in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0023] In order to solve the problems existing in the prior art, an embodiment of the present invention provides a low reactive power operation mode and method for a DC transmission converter valve.

[0024] An embodiment of the present invention provides a low reactive power operation mode of a DC transmission converter valve, wherein a bridge arm of the converter valve has a shutoff valve string, and the low reactive power operation mode is configured as follows:

[0025] The real-time on-current of the bridge arm of the converter is monitored in real time. When the real-time on-current of the bridge arm is less than the off-current, the corresponding shut-off valve string is shut off. When all the energy generated by the off-current on the commutation reactance is absorbed by the buffer capacitor, the maximum voltage of the buffer capacitor is equal to the arrester action voltage.

[0026] Optional, such as Figure 2 As shown, the converter includes multiple identical bridge arms, each bridge arm is composed of a switchable tube valve string, each switchable tube valve string is composed of m switchable tubes connected in series, m is a positive integer greater than 1, wherein the anode of the previous switchable tube is connected to the cathode of the next switchable tube to achieve series connection; wherein, the cathode of the switchable tube at the first end of the switchable tube valve string in the first bridge arm among the multiple bridge arms is connected to the positive electrode of the DC voltage, and the anode of the switchable tube at the second end of the switchable tube valve string is connected to the three-phase AC connection point; the cathode of the switchable tube at the first end of the switchable tube valve string in the second bridge arm among the multiple bridge arms is connected to the three-phase AC connection point, and the anode of the switchable tube at the second end of the switchable tube valve string is connected to the negative electrode of the DC voltage.

[0027] Among them, the switchable tube refers to a device with a self-shutdown function, that is, a power electronic device that can control the opening and closing of the device through a control signal.

[0028] Preferably, the turnable device may include, but is not limited to, GTO (gate turn-off thyristor), IGCT (integrated gate-commutated thyristor), IGBT (insulated gate bipolar transistor), GTR (power transistor), MOSFET (power field effect transistor), etc.

[0029] Optional, such as Figure 3 As shown, each bridge arm also includes a thyristor valve string connected in series with the turn-off valve string, each thyristor valve string is composed of k thyristors in series, k is an integer greater than or equal to 1, wherein the anode of the previous thyristor is connected to the cathode of the next thyristor to achieve series connection; wherein, in the first bridge arm of the multiple bridge arms, the cathode of the thyristor valve string is connected to the positive electrode of the DC voltage, and the anode of the thyristor valve string is connected to the cathode of the turn-off valve string; in the second bridge arm of the multiple bridge arms, the cathode of the thyristor valve string is connected to the three-phase AC connection point, and the anode of the thyristor valve string is connected to the cathode of the turn-off valve string.

[0030] The converter valve continuously operates in a low reactive power operation mode, which can shut down the current before it naturally crosses zero. Therefore, the converter valve arc extinction angle can be reduced to 0 or even a negative number, thereby reducing the reactive power demand of the converter valve and reducing the reactive power site of the converter valve.

[0031] Another embodiment of the present invention provides a method for low reactive power operation of a DC power transmission converter valve, such as Figure 1 As shown, the following steps are included:

[0032] Step S1: monitor the real-time conduction current of the bridge arm of the converter in real time.

[0033] Step S2: When the real-time conduction current of the bridge arm is less than the shutdown current, the corresponding shutoff valve string is shut off, wherein when the energy generated by the shutdown current on the commutation reactance is completely absorbed by the buffer capacitor, the maximum voltage of the buffer capacitor is equal to the arrester action voltage.

[0034] Specifically, Figure 4 As shown in the figure, at 400A, the shutdown overvoltage generated by the capacitor absorbing the shutdown energy is higher than the arrester action voltage, and there is a risk of continuous action of the arrester. However, at 250A, the shutdown overvoltage is lower than the arrester action voltage, so it can continue to act.

[0035] In the above method of this embodiment, the following steps are also included:

[0036] The cut-off current is determined according to the lightning protection action voltage of the converter valve, the commutation reactance and the capacitance of the buffer capacitor.

[0037] The above method of this embodiment monitors the real-time on-current of the bridge arm of the converter in real time. When the real-time on-current of the bridge arm is less than the off-current, the corresponding shut-off valve string is shut off, so that the current can be shut off before it naturally crosses zero. Therefore, the arc extinction angle of the converter valve can be reduced to 0 or even a negative number, thereby reducing the reactive power demand of the converter valve and reducing the reactive power station of the converter valve.

[0038] Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention shall still fall within the patent scope of the present invention.

[0039] Unless otherwise stated, the "connection" mentioned above refers to a logical relationship of current transmission, and does not necessarily mean a direct electrical connection. At the same time, "first", "second", etc. do not indicate a sequence, but are only used to identify related units, devices, etc.

Claims

1. A low reactive power operation mode of a DC transmission converter valve, characterized in that: The bridge arm of the converter valve has a shutoff valve string, and the low reactive power operation mode is configured as follows: The real-time on-current of the bridge arm of the converter is monitored in real time. When the real-time on-current of the bridge arm is less than the off-current, the corresponding shut-off valve string is shut off. When all the energy generated by the off-current on the commutation reactance is absorbed by the buffer capacitor, the maximum voltage of the buffer capacitor is equal to the arrester action voltage.

2. The low reactive power operation mode of the DC power transmission converter valve according to claim 1, characterized in that: The converter includes multiple identical bridge arms, each bridge arm is composed of a switchable tube valve string, each switchable tube valve string is composed of m switchable tubes connected in series, m is a positive integer greater than 1, wherein the anode of the previous switchable tube is connected to the cathode of the next switchable tube to achieve series connection; wherein, the cathode of the switchable tube at the first end of the switchable tube valve string in the first bridge arm among the multiple bridge arms is connected to the positive electrode of the DC voltage, and the anode of the switchable tube at the second end of the switchable tube valve string is connected to the three-phase AC connection point; the cathode of the switchable tube at the first end of the switchable tube valve string in the second bridge arm among the multiple bridge arms is connected to the three-phase AC connection point, and the anode of the switchable tube at the second end of the switchable tube valve string is connected to the negative electrode of the DC voltage.

3. The low reactive power operation mode of the DC transmission converter valve according to claim 2, characterized in that: Each bridge arm also includes a thyristor valve string connected in series with the switchable valve string, each thyristor valve string is composed of k thyristors connected in series, k is an integer greater than or equal to 1, wherein the anode of the previous thyristor is connected to the cathode of the next thyristor to achieve series connection; wherein, in the first bridge arm of the multiple bridge arms, the cathode of the thyristor valve string is connected to the positive electrode of the DC voltage, and the anode of the thyristor valve string is connected to the cathode of the switchable valve string; in the second bridge arm of the multiple bridge arms, the cathode of the thyristor valve string is connected to the three-phase AC connection point, and the anode of the thyristor valve string is connected to the cathode of the switchable valve string.

4. A method for low reactive power operation of a DC transmission converter valve, characterized in that: The method comprises the following steps: Real-time monitoring of the real-time conduction current of the bridge arm of the converter; When the real-time conduction current of the bridge arm is less than the shutdown current, the corresponding shutoff valve string is shut off, wherein when the energy generated by the shutdown current on the commutation reactance is completely absorbed by the buffer capacitor, the maximum voltage of the buffer capacitor is equal to the arrester action voltage.

5. The method for low reactive power operation of a DC power transmission converter valve according to claim 4, characterized in that: The following steps are also included: The cut-off current is determined according to the lightning protection action voltage of the converter valve, the commutation reactance and the capacitance of the buffer capacitor.

Images